Why Solar Permits Now Require a Roof Structural Letter
A growing number of AHJs across the US won't approve a solar permit on the racking attachment calcs alone anymore — they also want a separate letter confirming the existing roof framing itself can carry the added weight. Here's what that letter is, why it's showing up more often, and how to keep it from becoming a surprise mid-project.
What a roof structural letter actually is
It's a short, PE-stamped written evaluation — usually one to three pages — stating that the existing roof framing (rafters, trusses, sheathing, and their connections) can support the added dead load of a solar array, sometimes called an "engineering letter of adequacy" or "structural adequacy letter" depending on the jurisdiction. It's not the same document as the racking attachment calculations.
Structural letter vs. racking attachment calcs: two different questions
These get confused constantly because both involve structural engineering and both usually arrive in the same plan set. They answer two different questions:
- Racking attachment calcs answer: "Is the new hardware — rails, lag bolts, flashing, standoffs — strong enough to hold the panels to the roof?"
- Roof structural letter answers: "Is the roof itself — the trusses or rafters already up there — strong enough to carry that hardware, the panels, and any added snow/wind load, without exceeding its original design capacity?"
A roof can pass the first question and fail the second — new racking hardware rated for far more than the panel weight doesn't help if the trusses underneath were only ever designed for the original shingle load with no margin left over.
Why AHJs are asking for this more often
Aging housing stock
A large share of the US roof stock is 20-40+ years old. Original truss packages were sized for the roofing material at the time — plan reviewers are increasingly unwilling to assume decades-old framing has unused capacity without documentation.
Undocumented re-roofs
Re-roofing over an existing layer (or a second layer) adds dead load that may not appear in the county's permit history at all, especially on older homes. A structural letter forces a real look at current condition, not just the original as-built.
Heavier equipment on the roof
Battery-ready systems, larger modules, and dual-tilt racking on flat roofs all add more dead load than a standard rooftop array from a decade ago — AHJs in wildfire- and hurricane-code states in particular have tightened review as a result.
Liability, not just code
For the AHJ, a documented structural letter shifts liability for the "can this roof take it" question onto a licensed engineer's stamp — that incentive alone is pushing more jurisdictions to require it even where the base code is ambiguous.
Where this shows up most
| Region | Typical trigger |
|---|---|
| California | Homes 20+ years old, any tie-in requiring Title 24 review, flat/low-slope commercial roofs |
| Florida | Post-hurricane code enforcement, homes built before current wind load standards |
| Northeast (NY, MA, PA) | Snow load reassessment on older truss packages, especially with add-on dormers or additions |
| Puerto Rico | OGPe review of pre-code-update construction, especially post-storm re-roofs |
What the letter needs to include
- Framing identification: rafter or truss spacing, span, and species/grade (from visual inspection or as-built drawings)
- Existing load capacity: the roof's original design dead and live load, per the applicable code edition
- Added PV dead load: panels, racking, and any battery/ESS equipment mounted on the same structure
- Condition assessment: visible deterioration, prior modifications, or damage that could reduce capacity below the original design
- Conclusion: a clear pass/fail statement, with remediation notes (sistering rafters, added blocking, etc.) if the roof doesn't have margin as-is
Pro tip: Order the structural letter alongside your permit set from day one — not after an AHJ correction letter asks for it. Adding it after submission means a second review cycle and, if remediation is needed, a change to the installation itself.
What happens if the roof doesn't pass as-is
It doesn't necessarily kill the project. Common remediation the letter might call for: sistering additional rafters alongside existing ones, adding blocking between trusses at attachment points, or relocating array zones away from a weaker section of the roof (over a garage addition with a different truss package, for example). All of these are far cheaper to catch before installation than after a failed final inspection.
Every EnersolConnect plan set includes the structural review needed for the project's jurisdiction — including a roof structural letter where the AHJ requires one, so it's accounted for in the first submission instead of a second one. Get a quote →